1. Field of the Invention
The present invention relates to the field of a microbial fuel cell. In more particular, the present invention relates to a module system for a microbial fuel cell in which a plurality of unit cells electrically connected to each other in series cannot share an anode part solution.
2. Description of the Related Art
In general, an MFC (microbial fuel cell) is a device to convert chemical energy of a substrate oxidized through the metabolism of microorganisms into electrical energy. The MFC is mainly classified into two parts of a cathode and an anode. Both the cathode and anode must be separated from each other by an ion exchange membrane such that the cathode and anode electrodes may not come into contact with each other (see FIG. 1). According to the operating principle of the MFC, the substrate (mainly, organisms) in the substrate solution is oxidized by the microorganisms of the anode to produce electrons and hydrogen ions, and the electrons and the hydrogen ions are transferred to the cathode through an external circuit and the ion exchange membrane, respectively. Thereafter, the hydrogen ions transferred through the ion exchange membrane react with oxygen molecules supplied to the cathode and the electrons transferred to the cathode so that the hydrogen ions are reduced, thereby constructing a whole circuit. Therefore, the cell potential obtained through the MFC is given as the difference between the potential produced when the substrate is oxidized in the anode and the potential produced when an oxidizer is reduced in the cathode. Theoretically, energy can be continuously acquired through the electrochemical reaction if the substrate capable of maintaining the basal metabolism of the microorganisms is continuously supplied
The electricity generation using the microorganisms has been spotlighted since the possibility of electricity production using colon bacillus (E. coli) has been verified in 1911 (Potter, 1911). A microbial cell capable of producing electricity of 35V or more in the case of in-series connection has been developed in 1931 (Cohen, 1931), and a hydrogen-air fuel cell using hydrogen, which is produced by fermenting glucose by microorganisms, as fuel has been developed in 1963 (DelCuca et al., 1963). However, the hydrogen-air fuel cell produces unstable current because a uniform amount of hydrogen is not produced by the microorganisms. In order to solve the problem, clostridium bytyricum, which is a bacterium to produce hydrogen, has been fixated on an electrode to produce stable current 1976 and 1977 (Karube et al., 1976, 1977). Since bio-fuel cells have been newly spotlighted in the late 1980, electricity production using microorganisms such as E. coli, anabaena variabilis, and proteus vulgaris in a fuel cell having a mediator acting as an electron shuttle has been attempted (Allen and Bennetto, 1993; Sell et al., 1989; Tanaka et al., 1988). The mediator is a material to promote the electron transfer from the outer skin of a bacteria cell having a non-conductive property to an anode. The mediator is reduced by electrons produced when microorganisms oxidize an organic compound, and then oxidized in the anode again to transfer electrons to the anode. As the mediator, methylene blue (Roller et al., 1984), thionine (Bennetto et al., 1985), 2-hydroxy-1,4-naphtoquinone (Akiba et al., 1985), and viologens (Akiba et al., 1985; Roller et al., 1984) have been extensively known. However, 100% of the mediators are not retrieved in the cell of the microorganism. Accordingly, when the mediators are used, the mediators must be continuously supplemented to enhance the efficiency of the fuel cell. When the mediators are continuously supplemented, the mediators accumulated in the cell of the microorganism act as toxic material against the microorganism, thereby stopping the metabolism of the microorganism, so that electricity production cannot be performed for a long time. The problem related to the mediator is solved by verifying the possibility of the electricity production by using shewanella putrefaciens which are bacteria having a mechanism to reduce insoluble ferric oxide outside a cell through an outer cell membrane based on reducing power generated through energy metabolism (Kim et al., 1999). After the applicability of the shewanella putrefaciens has been verified, the researches and studies on the microbial fuel cell have been more accelerated.
With the studies for the improvement in the efficiency of the electricity generation by the microbial fuel cell, the trials to produce power in a commercial scale by improving the output of the microbial fuel cell have been continuously performed. In order to generate power in the commercial scale as described above, the generated power must be increased and the loss of the power must be minimized. In addition, the system for the microbial fuel cell must be scaled up. Therefore, a system for a microbial fuel cell without voltage drop in a simple structure is strongly required.